1. Field of the Invention
This invention relates generally to the projection of images on a viewing screen, and more particularly is directed to improvements in image projection apparatus of the type in which images, for example, in the form of letters, indicia and/or patterns, produced by an image reproducing device, such as, a Braun or cathode ray tube, are projected through a projection lens onto a viewing screen for providing an enlargement of the reproduced image on the screen.
2. Description of the Prior Art
It has been proposed to provide an apparatus in which an image produced by a Braun or cathode ray tube or other image reproducing device is projected through a lens onto a viewing screen so as to provide an enlarged reproduced image on such screen. However, with such previously proposed apparatus, there is inadequate contrast between the projected image and the background or field of the viewing screen so that it is difficult to distinguish the projected image from the background or field, particularly when ambient illumination falls on the viewing screen. Further, if the reproduced images are to be of various colors so that the image reproducing device is in the form of a color cathode ray tube having a color phosphor screen and an associated shadow mask, such shadow mask inherently reduces the brightness of the reproduced image, and hence of the image projected on the viewing screen, so that the problem of distinguishing the projected image from the background or field of the viewing screen is aggravated.